The art of sound coding, transmission, recording, mixing and reproduction has been a continuous topic of research and development for many decades. Starting from the monophonic technology, technologies on multichannel audio have been gradually extended to include stereophonic, quadrophonic, 5.1 channels and the like. Compared with traditional mono or stereo audio, multichannel audio provides end users with a more compelling listening experience and, thus, becomes more and more appealing to audio producers.
For multichannel audio to be successful it should be possible to reproduce multichannel audio on a legacy playback device supporting only a subset M of an arbitrary number of recording channels Q. The subset of M reproduction channels, for instance, loudspeakers or headphones, in the playback device may change according to the user's need. This may happen when the user switches his device, e.g., from stereo to 5.1 or from stereo to any 3 loudspeaker devices.
The conventional way of reproducing multichannel audio on a legacy playback device is by using a fixed downmix matrix for downmixing the Q channel audio input signal into an audio output signal having only M channels. This can be done at the sender or the receiver side, which is constrained by the popular content format available, such as stereo, 5.1 and 7.1. To date, it is not possible for any playback device to support an arbitrary number of output channels in an optimal and flexible way without prior information regarding the reproduction layout, no feedback to recording device, e.g., plug and play stereo to 3.0, stereo to 8.2, etc.
Thus, there is a need for an improved audio signal processing apparatus and method, in particular an improved audio signal processing apparatus and method allowing for an adaptive reproduction of an audio output signal.